Even with all of the inherent advantages of solid-state, disk-based optical data drives and magnetic hard drive storage technology, there’s still no more cost-effective alternative for long-term archiving than tape. A linear tape-open (LTO) data tape cartridge, that is.
That’s the opinion of many, including Dr. Philip Storey, co-founder and CEO of XenData and a veteran of the archive storage industry. Xendata, based in Walnut Creek, CA, makes special software that manages data tape libraries (from companies like Rorke Data) for archiving using LTO-4 and soon LTO-5 tapes. Most LTO tape drives are currently manufactured by Hewlett Packard and IBM and all are backwards compatible with the last two LTO generations, making the reading of older tapes possible without newer hardware or file conversion.
“There’s no doubting that LTO tape is extremely cost effective, especially if tapes are going to be placed on a shelf somewhere,” Storey said. “I think the jury is still out on whether solid-state will be a viable archival media in the future. And it has to do with more than just price.”
Indeed, the cost difference is significant. A single LTO-4 tape offers about 800GB of capacity, costs about $50 and has a shelf life of around 30 years. The cost of LTO-4 data tape ($50) works out to about six cents per GB, as compared with $3 per GB for solid-state media. LTO-5, set to ship in Q2 of 2010, will offer 1.5TB per tape, for storing about 15 100GB files. They are expected to cost about $120 per disc initially.
Also, no one to date has been able to clearly identify the shelf life of other high-capacity storage media. For example, there are some concerns about the security of the data with solid-state over time. It’s basically a charge on a silicon semiconductor, which has been known to dissipate with time.
“We know there are very little issues with taking a physical LTO tape and putting it on a shelf for a very long time; solid-state still makes many librarians nervous,” Storey said.
Solid-state drives are starting to emerge as a rugged alternative to magnetic disc drives in laptops and other portable devices, but at the enterprise level, there are issues to be resolved because the IT managers are conservative when it comes to data reliability and their capital expenditures.
Then there’s optical storage, but according to Storey, media like DVD and Blu-ray are pushing their capacity limits, but are good for file distribution and low-end archiving. The format is limited by the finite size of a focused blue laser beam and the only option to increase capacity is to add layers. (Dual-layer discs are now readily available that offer 50GB of storage capacity, for about $60.) Larger video files are also accessed faster from an LTO tape than it is from an optical disc because of the high transfer rate from LTO. Storey said that LTO tape is still preferred among broadcasters and content distribution companies for high performance video archiving because of performance, cost and longevity.
“We continue to look at all of the available and emerging technologies and keep coming back to tape as the best video storage option for performance and capacity,” Storey said. “We’ve got customers who have files in excess of 1000Mb/s, so anything short of 2000GB just won’t be adequate in today’s HD environments.”
This includes alternatives like holographic optical data storage and cloud storage (which uses an off-site archive to store material). Both have also been slow to be adopted by broadcasters and media companies in any meaningful way — due to capacity (optical) and security and bandwidth issues. Storey, who received his PhD in holography 25 years ago, said that the problem with all types of optical storage, in general, is that the laser beam that reads and writes the data is relatively big.
He said dual-layer Blu-ray is the best optical storage available today, but to increase capacity, you have to add more layers, which makes reading/writing to the disc difficult. Holographic suffers from the same limitations. You can't write anything smaller than one-third of a micron, which limits the capacity of reach layer.
“This is why we haven’t seen any real deliveries of holographic storage systems to date,” Storey said. “The reality is that it’s difficult to do and keep stable. This issue of ‘crosstalk’ between layers has been talked about for years, and as we sit here today, tape is still what our customers want most. And there’s a roadmap to get at least 3TB of capacity on a single tape. I’m still waiting for a better format, but there isn't one.”
As for system cost, Storey said a complete digital file archive server could be installed with Xendata file management software, standard IT hardware for about $25,000-$30,000, which offers a nearline storage capacity of 20TB and unlimited capacity from managed tapes that are held “on the shelf.”
With Xendata software, the archive appears as a standard file system; it is just like a server on the network with a high-capacity RAID. A file is first saved to disk storage on the archive and then saved off to LTO tape within a robotic tape library. Depending upon when that file will be used again, it might be automatically removed from the disk, but will still be available for restore from LTO. File permissions are maintained, which means each file can be electronically marked to limit access to authorized personnel.
Some broadcasters set policies on the archive to write to duplicate LTO cartridges for redundancy and data protection. As the tapes become full, they will export one of the duplicates from the tape library and store it in a safe location for disaster recovery. Also, if the need to access some video files becomes infrequent, both of the duplicates can be exported taking the file contents offline. If there is an attempt to access an offline file, the XenData software provides an on-screen message and will send an e-mail to the librarian identifying which tape bar code should be selected and put back into the tape library.
Stations such as KATV-DT, the ABC affiliate in Little Rock, AR, and KVIE, a PBS station in Sacramento, CA, use the system. KVIE installed a XenData LTO archive system about three years ago, in tandem with a Rorke Data 264 slot robotic tape library. This was initially used to archive video files from an NVerzion automation system. The KVIE archive is now also used with Apple Final Cut Server, which provides media asset management. The Web site TMZ.com also uses Xendata for archiving its thousands of digital files, in tandem with a Dalet news editing platform.
In terms of long-term archives, it’s important that data is stored in such a way that it can be read for many years to come. To ensure access to the material, companies like Xendata record data on the tape in the POSIX “tape archive” (tar) format, which has become an industry standard (although not every archive vendor does this, instead using proprietary schemes). The tar format was first introduced by AT&T in 1979 and is still supported today.
“Today you can take a Xendata tape that was written in the past and use a current LTO tape drive to read it,” Storey said. “When you store data on other media or on data tape without using tar, that may not be the case. And what good is material stored on a media of you can’t access it. You don't want to be locked into a proprietary format, ever.”
For all types of archiving, affordability is the key. Early next year (see them at NAB in April), Xendata will release a new single-drive LTO tape archiving system for smaller stations and post-production facilities.
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